1. Field of the Invention
This invention relates to filtering apparatus and, more particularly, to the separation of the process liquid from contaminants which are accumulated in the liquid by means of filtration, including solids added to such liquids to aid filtration, such as diatomite powder.
2. Description of the Prior Art
A major problem in the operation of any industial process using a recirculating liquid relates to filtration of the process liquid. Very often the endurance of the process or the length of time that the process can be conducted without interruption will depend upon the capacity of the filtering apparatus. As the filtering apparatus accumulates contaminants, the filters will eventually clog. The filter will then have to be taken off line in order to be cleaned.
In the past, such off line cleaning procedures have often included disassembling of the filter to change the filter elements. Where permanent type filter elements are used, some form of a blow down and/or reverse flushing of the filters occurs to clear the contaminant particles from the filter and allow for recirculation of the process fluid. The blow-down and/or reverse flush of the filters often requires relatively high positive pressures within the filers to create the appropriate pressure gradient necessary to dislodge the particles from the filter elements. Further, these blow down cycles often are extended in duration requiring that the filtering apparatus be removed from on line duty for as long as 48 hours or more. This is especially true of filters which embody a "sub-filter" of felt, paper, cloth or other permeable material on their floor.
Because compressed air is often used in the blow-down cycles, it is necessary to construct such filters to comply with codes and stress requirements of pressure vessels whose operating pressures are substantially higher than the pressures at which these filters perform their filtering function.
Additionally, problems have existed with separating the contaminant particles that have been removed by the filters from the recirculating fluid after the particles have been back washed from the filter. Very often the system recirculating fluid will be a volatile hydrocarbon fluid and the mixture of the fluid and the large concentration of contaminating particles referred to as a sludge cannot be easily separated other than by a distilling process to recapture the recirculating fluid. This, therefore, requires a separate piece of equipment for distilling often flammable fluids and, therefore, introduces additional hazards and safety requirements which must be carefully followed.
Further, because of the volatility of the process liquid, the distilling apparatus must often be certified for positive pressure safety levels. Therefore this apparatus must often be built in conformity with boiler safety codes or other codes that render their fabrication relatively expensive.
Also, in the distillation process substantial amount of these fluids can be lost, and the sediment is often affected by the distillation process.